Electrohydraulic control arrangement for hydraulic actuators

ABSTRACT

A control arrangement for hydraulic actuators in which two hydraulic transmission lines communicating with the actuator are closed when the control slide of a control valve is in neutral position. Inlet and return lines communicate with the hydraulic transmission lines in alternate operative positions of the control slide. The control slide is actuated by a piston moving within a control cylinder. Working fluid is applied to the control cylinder through electromagnetically actuated valves. A remote control lever provides an adjustable input parameter through a transducer. The electromagnetically actuated valves are operated by a regulating amplifier as a function of the input parameter established by the remote control lever. Two flow lines communicate with the control cylinder and are connected to the inlet and return lines by two electromagnetically actuated valves. Threshold switching circuits are connected between the signal amplifiers used to energize the electromagnetically actuated valves and the regulating amplifier.

United States Patent 1 Mindner et al.

[ Nov. 27, 1973 ELECTROHYDRAULIC CONTROL ARRANGEMENT FOR HYDRAULICACTUATORS Filed: April 11, 1972 Appl. No.: 239,396

Primary ExaminerHenry T. Klinksiek Assistant ExaminerRobert J. MillerAttorney-Striker, Striker, Kontler & Stenby [57 ABSTRACT A controlarrangement for hydraulic actuators in which two hydraulic transmissionlines communicating with the actuator are closed when the control slideof a control valve is in neutral position. lnlet and return linescommunicate with the hydraulic transmission lines in alternate operativepositions of the control slide. The control slide is actuated by apiston moving within a control cylinder. Working fluid is applied to thecontrol cylinder through electromagnetically actu- Foreign ApplicationPriority Data ated valves. A remote control lever provides an adjust-Mar. 26, 1971 Germany P 21 14 639.4 able input parameter through atransducer. The elec- I tromagnetically actuated valves are operated bya reg- [52] U.S. Cl. l3 7/625.64 'ulating amplifier as a function of theinput parameter [51] Int. Cl. F16k 11/00 established by the remotecontrol lever. Two flow [58] Field of Search l37/625.64, 625.66, linescommunicate with the control cylinder and are 137/625.65, 625.69, 554,487.5; 251/131, connected to the inlet and return lines by two electro-251/130, 14, 25, 63, 78 magnetically actuated valves. Thresholdswitching circuits are connected between the signal amplifiers used [56]References Cited to energize the electromagnetically actuated valvesUNITED STATES PATENTS and the regulating amplifier- 3,556,l54 l I971Kramer 137/625.64 17 Claims, 5 Drawing Figures T M W5 Q 20 1 /7 26 a T 14 211 t/i3 5 f I r J Ulla P .52 l y 35 .40 42 [A AA A Q .14 fi r 1 .U U

ELECTROHYDRAULIC CONTROL ARRANGEMENT FOR HYDRAULIC ACTUATORS BACKGROUNDOF THE INVENTION The present invention relates to an electrohydrauliccontrol arrangement for use in conjunction with a hydraulic actuatorwhich is operable in two directions. A control valve is provided with acontrol slider which closes two lines to the actuator when in neutralposition. A regulating amplifier controls the precontrol valves as afunction of an input parameter set by a remote control lever.

A control arrangement of the preceding known species is already known inthe art for actuating the altitude rudder or flaps of an aircraft. Insuch an arrangement known in the art, the output parameter or value fromthe deflection angle of the rudder is applied to a second input of theregulating amplifier, so that for every position of the remote controllever, a predetermined deflection angle of the rudder is attained. Inother hydraulic actuators, as for example in automotive cranes, whichare driven by double acting hydraulic cylinders or by a hydraulic motorwith radial head, it is desired, however, to regulate the velocityrather than the final position.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a control arrangement in which a predetermined velocity of thehydraulic actuator corresponds to every position of the remote controllever. In the use of an automotive crane, for example, the velocity ofthe load fork or distributor is to be set or established.

Another object of the present invention is to provide an arrangement forcontrolling a hydraulic actuator, as set forth, which is simple anddesign and may be readily fabricated.

A still further object of the present invention is to provide anarrangement of the foregoing character which may be economicallymanufactured and economically maintained in service.

Another object of the present invention is to provide an arrangement ofthe foregoing character which is reliable in operation.

The objects of the present invention are achieved by providing that thecontrol cylinder is in the form of a double acting cylinder with twocommunicating lines. A second and a third precontrol valve connect thetwo communicating lines with inlet and return lines. Each precontrolvalve may be actuated through a magnetic winding which, in turn, isenergized by a signal amplifier. The signal amplifiers are connected,through threshold switching circuits, to the output of the regulatingamplifier.

In an automotive crane it is advantageous when the operating personnelof the crane, can operate the crane directly when on the vehicle for thecrane, as well as from a remote location through a cable. Suchpossibility is realized with a further embodiment of the presentinvention, in which a first precontrol valve lies between the inlet lineand the two other precontrol valves. The first precontrol valve isclosed when the remote control lever is in its position. When the firstprecontrol valve is closed, furthermore, the control slide may beactuated by a close control lever.

The velocity of the hydraulic actuator or operating arrangement may beprecisely regulated or set, in accordance with a further embodiment ofthe present invention, by providing that an output parameter or valuetransducer may be actuated by the control slide. The output transducerand the input transducer are both connected to a summing device in frontof the regulating amplifier.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic diagram of thehydraulic arrangement in conjunction with the electronic controlcircuitry, in accordance with the present invention;

FIGS. 2-4 are electrical circuit diagrams of operating circuits shown inblock form in FIG. 1;

FIG. 5 is a block diagram of a second embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing and inparticular to FIG. 1, a hydaulic operating unit has a double-actingcylinder 11 in which a piston head 12 moves with a piston rod 13. Thecylinder 11 is connected to a control valve through lines 14 and 15.Within a housing 16 of the control valve, is a slider bore 17 whichguides closely a control slide 23. The slide bore 17 communicates withfive chambers 18, 19, 20, 21, 22 and a control cylinder 27. The centralchamber 20 is connected with an inlet line 57 through a check valve 33.The two chambers 19, 21 on both sides of a central chamber 20, areconnected with the lines 14, 15, while the outer chambers l8, and 22 areconnected to the return line 37.

The control slide 23 is subdivided into three slider sections by twonecked-down portions 24, 25. In the neutral position of the controlslide 23, the three slider sections lie closely opposite the chambers 18to 22, as shown in FIG. 1. At the right end of the control slide 23, isa control piston head 26 which is designed in the embodiment in the formof a differential piston, and is movable within the control cylinder 27.At the left end of the control slide 23, is an extension 29 whichactuates, on the one hand, a double-acting return or resettingarrangement. This extension 29 also is connected, on the other hand,mechanically with a control lever 30 and an output transducer 47.

The inlet line 57 is provided with'pressurized fluid from a storagereservoir 31, by means of a pump 32. A hydraulic series-connectedcircuit between the inlet line 57 and the return line 37, consists ofthe series combination of a first control valve 34, a first throttle 35,a second control valve 36, a third control valve 38, and a secondthrottle 39. The control cylinder 27 is, on one hand, connected througha first line 58, to the connecting line between the first control valve34 and the first throttle 35. The control cylinder 27 is also connected,on the other hand, through a line 59, to the connecting line between thesecond control valve 36 and the third control valve 38.

The control valves 34, 36 and 38 become actuated by the electromagnetwindings 34a, 36a. and 38a. Each winding becomes controlled from anamplifier 40, 41, 42, respectively.

A remote control lever 55 actuates an input transducer 48 which has anoutput connected to a deadcenter element 50, through an amplifier stage49. Connected with the output of the dead-center element 50, are thefirst inputs of three AND-gates 43, 44 and 45. These AND-gates are, inturn, connected to amplifiers 40, 41 and 42, with their outputs. Thesecond input of the first AND-gate 43 is connected, through a fourthAND-gate 46, with the outputs of the second and third AND-gates, 44 and45, respectively. The AND-gate 46 is constructed in the form of aNAND-gate.

The second inputs of the second and third AND-gate 44, 45 are connectedeach, by way of threshold switches 53, 54, to the output of a regulatingamplifier 52. A summing device 51 is connected to the input of thisregulating amplifier 52. The input transducer 48 and the outputtransducer 47 are connected to the inputs of the summing device 51.

FIG. 2 shows the circuit diagram of the second threshold switch 54, thethird AND-gate 45 and the third amplifier 42. The second thresholdswitch 54 is designed in the form of a two-stage, feedback-coupledamplifier with two transistors 540, 541 of opposite conductivity type.The first transistor 540 has a base voltage divider 546, 547, anemitter-resistor 544, and a collector resistor 542. The collector of thefirst transistor 540 is connected to the base of the second transistor541. The collector of the second transistor 541 is connected, through afeedback resistor 545, to the base of the first transistor 540. Thiscollector of the second transistor 541 is also connected, through acollector resistor 543, to the positive voltage supply line 60. Theemitter of the first transistor 540 forms the input of the secondthreshold switch 54, and is connected, through a diode 548, to theoutput terminal 52a of the regulating amplifier 52.

The third AND-gate 45 is similar to the second threshold switch 54 inthe form of a feedback-coupled amplifier with two transistors ofopposite conductivity type. Modifications in the circuit design arerealized in the respect that the third AND-gate 45, as shown in FIG. 1,is designed in the form of a blocking or inhibiting gate which has anoninverting and one inverting input. In addition, the second transistor451 in the third AND-gate 45, has two collector resistors 453, 453aconnected in series. The junction of these two resistors is connected tothe second noninverting input of the third AND-gate 45. This junction,furthermore, is connected through a diode 458, to the output of thesecond threshold switch 54. All remaining components are the same as inthe second threshold switch 54, and are thereby not further described.The reference numerals are lower by 90, than in the second thresholdswitch 54.

The third amplifier 42 has a transistor 420 and a power transistor 421.The preamplifying transistor 420 is connected with its base, to theoutput of the third AND-gate 45. The emitter of the preamplifyingtransistor 420, is connected, through a diode 424, to the negativevoltage supply line 62. The collector of this transistor 420,furthermore, is connected through two resistors 422, 423, to anonstabilized positive voltage supply line 61. The base of the powertransistor 421 is connected to the junction between the resistors 422and 423. The emitter of the transistor 421 is connected directly withthe non-stabilized voltage supply line 61.

The collector of the power transistor 421 is connected, furthermore,through a resistor 425 and electromagnetic winding 38a, to the negativevoltage supply line 62. A series circuit, moreover, leads from thecollector of the power transistor 421, to a diode 428 and a resistor427, and from there to the negative voltage supply line 62, as well as ajunction to the feedback resistor 455 within the third AND-gate 45.Connected in parallel with the resistor 425, is a storage capacitor 426.

The remaining AND-gates 42, 44 and 46, as well as the first thresholdswitch 53 are constructed precisely the same as the second thresholdswitch 54. The latter is universally insertable, since it is possible toconnect as many inputs as desired, to the emitter of the firsttransistor, through diodes. At the same time, the threshold level can beset simultaneously with the aid of the base voltage divider of the firsttransistor.

The dead-center circuit 50, shown in FIG. 3, consists of two thresholdswitches 505, 506 which are also constructed and designed in the formdescribed above. The threshold level of the switch 505 is set at 7volts, in the embodiments, and the other threshold switch is set to 5volts. The output of the switch 505 is connected, through a diode 503,to a second output of the other threshold switch 506. With thisarrangement, a positive signal is emitted at the output terminal 50a ofthe deadcenter circuit 50, when the input voltage at the terminal 49a iseither below 5 volts or above 7 volts. Within this region, the outputterminal 50a is substantially at the potential of the negative voltagesupply line 62.

FIG. 4 shows the circuit diagram of a pulse stretcher modulator, whichcan be used in place of the threshold switch 53 or 54. an operationalamplifier 530 serves as the active component, and has a noninvertinginput at the junction of two resistors 533, 534, which form a voltagedivider. The inverting input of this operational amplifier 530, isconnected, through an input resistor 537, to an input terminal 52a. Aresistor 531 is connected between the output of the operationalamplifier 530 and the inverting input of the amplifier. A resistor 532,furthermore, is connected between the output of the operationalamplifier 530, and the noninverting input. The output of the operationalamplifier 530 is, furthermore, connected directly to an output terminal53a, and to the positive voltage supply line 60, through a resistor 536.A capacitor 535 is connected between the inverting input of theoperational amplifier 530, and the negative voltage supply line 62.

The second embodiment shown in FIG. 5, is extensively the same as thefirst embodiment. The components and circuits that are the same in FIG.5, as they are in FIG. 1, have the same reference numerals, and are alsonot further described. In the second embodiment, the first AND-gate 43has four inputs, of which two are connected the same as in the firstembodiment. The other two inputs of the first AND-gate 43 are connectedwith the outputs of a first OR-gate 73 and a second OR-gate 75. A thirdthreshold switch is connected to the output of the output transducer 47,and a fourth threshold switch 71 is connected to the output of thesumming device 51. A first inverter 72 is connected to the output of thethird threshold switch 70, and a second inverter 74 is connected to thefourth threshold switch 71. The two inputs of the first OR-gate 73, areconnected with the output of the first inverter 72 and the output of thefourth threshold switch 71. In a similar manner, the two inputs of thesecond OR-gate 75 are connected to the output of the third thresholdswitch 70 and the output of the second inverter 74.

For the purpose of describing the functional operation of theelectro-hydraulic control arrangement, the arrangement of the hydraulicvalves is described first. Each position of the control slide 23corresponds to a predetermined fluid flow from the inlet line 57 to oneof the lines 14, 15. With this arrangement, a predetermined speed orvelocity of the piston head 12 can be established corresponding to apredetermined position of the control slide.

The control valves 34, 36, 38, each have two controlled connections andtwo positions, and are thereby constructed in the form of 2/2-wayvalves. In the normal inoperative position, the first control valve 34is closed, and the two other control valves 36, 38 are open. It ispossible, thereby, to bring the control slide 23 into any desiredposition, with the aid of the control lever 30. As a result, any desiredvelocity of the operating piston head 12 may be attained. Should thecontrol slide 23 be actuated through the electro-hydraulic remotecontrol unit with the aid of the remote control lever 55, then the firstcontrol valve 34 becomes opened. When the control piston 26 is to bemoved toward the left, then the third control valve 38 must be closed,and the second control valve 36 must be opened. In the reversesituation, the second control valve 36 must be closed and the thirdcontrol valve 38 must be opened, in the case that the control piston 26is to be moved toward the right. When, finally, the control piston 26 isto be held at a predetermined position outside of its neutral position,then the second control valve 36 and the third control valve 38 must beclosed.

These four different valve positions are set or established by theelectronic circuit in dependency on the position of the remote controllever lever 55 and the output signal of the output transducer 47. In thefollowing description of the functional operation, the digital circuitryis described in conjunction with the designations of a 1 signal and 0signal as in common usage. When an AND-gate provides a 1 signal, it isimplied that its output is substantially at the potential of thepositive supply line 60. Conversely, when the output of the AND-gateemits a 0 signal, then the potential of the output of the AND-gate issubstantially at the negative voltage supply line 62. The outputtransducer 47, the input transducer 48, the amplifying stage 49 and theregulating amplifier 52, all provide analog signals. These analogsignals are converted to digital signals in the dead center circuit 50,as well as in the two threshold switches 53, 54. The remaining circuitryoperates, then, on the basis of only digital signals.

The summing device 51 is designed so that the output signal of the inputtransducer 48 is negative, and the output signal of the outputtransducer 47 is positive. This summing device 51, therefore, computesthe difference between the input value and the output value as providedby the transducers. In a practical design, the input transducer 48 andthe output transducer 47 are connected to the two inputs of a differenceamplifier, which serves simultaneously as the regulating amplifier 52.It is also possible to design the regulating amplifier 52 so that thelatter has an input, as shown in FIG. 1. With such an arrangement, aninverting stage must be connected to either the output of the inputtransducer 48 or the output of the output transducer 47. Such inversionis required in the event that the transducer does not provide alreadysuch an inverted signal, relative to the other transducer. Once suchinversion has been realized the two signals from the two transducers maybe applied, through summing resistors, to the input of the regulatingamplifier 52.

The input transducer 48 and the output transducer 47 are designed sothat their output potentials become shifted in the negative region, whenthe associated control lever is moved toward the left. The dead-centercircuit 50 provides a 0 signal within a-small region about the 0position of the remote control lever 55 within the so-called dead zone.In all other positions of the remote control lever 55, a 1 signal isemitted. In the embodiment, the threshold level of the first thresholdswitch 53 is set to 5 volts, and the second threshold switch 54 is setto 7 volts. At the same time, the output voltage from the regulatingamplifier 52 is established at 6 volts, provided the difference betweenthe input value and output value is zero. When the input value is equalto the output value, the first threshold switch 53 provides a 1 signal,and the second threshold switch 54 provides a 0 signal.

When the remote control lever 55 is moved toward the right, then thedead-center circuit 50 provides a 1 signal, when the dead zone isexceeded. The output voltage from the regulating amplifier 52 isshifted, thereby, in the positive direction to the extent that thethreshold level of the second threshold switch 54 becomes exceeded. Atthis point, the three circuits 50, S3, 54 each provide a 1 signal. Atthe output of the second AND-gate 44 is a 1 signal and at the output ofthe third AND-gate 45 is a 0 signal. At the output of the NAND-gate 46,is, thereby, a 1 signal which is applied to the second input of thefirst AND-gate 43. A 1 signal is, henceforth, also available at theoutput of the AND- gate 43. As a result, the first two control valvesbecome actuated by the amplifiers 40 and 41. The control piston 26moves, consequently, in the same direction as the remote control lever55namely toward the right.

In view of this arrangement, the output potential of the outputtransducer 47 is shifted in the positive direction, and the outputpotential of the regulating amplifier 52 is shiftedin the negativedirection, until the threshold level of the second circuit 54 is higher.Then the third AND-gate 45 also provides a 1 signal which, in turn,actuates the third control valve 38 and, at the same time, the AND-gate43 by way of the NAND-gate 46. The first amplifier 40 of the firstcontrol valve is thereby switched off. As a result, some control valvesare now closed, so that the control piston 26 becomes blocked in itsposition. A predetermined velocity of the operating piston 12 is therebyestablished, and this piston 12 corresponds precisely to the position ofthe remote control lever 55, as is required.

If, now, the remote control lever 55 is moved toward the left, then,after passage through the 0 region and the dead zone, the thresholdlevel of the first switch 53 becomes the higher value. Both thresholdswitches provide, thereby, 0 signals. Since the third AND-gate 45 isconstructed in the form of a blocking or inhibiting gate and is providedwith an inverting input, the output of this AND-gate 45 provides a 1signal which is applied to the third amplifier 42 and thereby the thirdcontrol valve 38. As a result, this valve 38 is closed. Since the secondcontrol valve 36 becomes simultaneously opened, through the AND-gate 44and the amplifier 41, and the first control valve 34 also becomes openedthrough the NAND-gate 46, the AND-gate 43 and the amplifier 40, thecontrol piston 26 is moved toward the left.

In summary, the functional operation of the first embodiment can bedescribed with the following characteristics: When the remote controllever 55 is deflected past the dead zone, either the second controlvalve 36 or the third control valve 38 is closed, depending upon thedirection of deflection of the lever. Aside from this, the first controlvalve 34 becomes opened, through the AND-gate 43 and the NAND-gate 46.When the remote control lever 55 is deflected, the first control valve34 is again closed, through the NAND-gate 46, only until the two othercontrol valves 36 and 38 are simultaneously closed, when the input valueis equal to the output value and the control piston 26 is to be held inits position.

A particular advantageous of the control arrangement described aboveresides in the condition that all digital components of the circuitrycan be constructed from the same circuit elements, as shown in FIGS. 2and 3. In the second threshold switch 54, according to FIG. 2, the basevoltage divider 546, 547 of the first transistor 540, is adjusted sothat a voltage of 7 volts is available at the tap. The first transistor540 becomes then turned off, as soon as the potential of the inputterminal 52a drops below 7 volts. The voltage drop across the diode 548and the emitter-base diode of the first transistor 540 becomecompensated. As a result of the positive feedback coupling of theresistor 545, no continuous collector current of the first transistor isavailable when the potential of the input terminal 52a is slowly takenoff. Instead, a rapid switching takes place in the threshold voltageestablished by the base voltage divider. From the circuit of thethreshold switch 54, a NAND-gate can be produced in a simple manner, inthat several input terminals can be connected to the emitter of thefirst transistor 540, by way of several diodes. Such a NAND-gate 506 isshown in FIG. 3 as a component of the dead-center circuit 50. A blockingor inhibiting gate with an inverting and a noninverting input, asrequired for the third AND-gate 45, is obtained when the emitter of thefirst transistor 450 is used as the first input and the collector of thesecond transistor 451 is used as the second input, as shown in FIG. 2with respect to the blocking gate 45.

The emitter potential of the transistor 420 in the second poweramplifier 42 is raised by substantially 0.7 volts, through the diode424, relative to the potential of the negative voltage line 62. In thismanner, the transistor 420 is securely turned off when the transistor451 conducts. Power transistor 421 is also turned off, since the latteris of opposite conductivity type relative to the transistor 420. Infront of the electromagnetic winding 38a, is the parallel circuitincluding the resistor 425 and the capacitor 426. Upon turning on thepower transistor 421, full operating voltage is applied, through thecapacitor 426, to the winding 38, until the capacitor 426 has becomecharged. As a result, a rapid energizing of the magnet winding 38a isrealized. After switching off the power transistor 421, the energystored within the winding 38a is dissipated in the two resistors 427 and425, and the resistance within the winding 38a. This results from thecondition that the tum-off current of the winding 38a can flow furtherthrough the diode 428.

The dead zone is the allowable deviation or difference between the inputvalue and output value, or is the region in which the output signal fromthe switch 53 is a 1 signal and the output from the switch 54 is a 0signal. The dead zone is provided so that continuous switching oroscillation of the valves is prevented. The dead zone together with thedead time of the control valves, determines the maximum allowabledisplacement velocity of the control slide 23. This velocity isdependent on the pressure in the inlet line 57, the dimensions of thethrottles 35 and 39, and on the surfaces of the control pistons. Thedisplacement velocity and thereby the acceleration of the operatingpiston 12, is thereby constant. As a result, reverse accelerations ordelays arise under predetermined conditions, when the remote controllever 55 is deflected, or when the input value is attained by the outputvalue. These displacement transitions become softer when the twothreshold circuits 53, 54 become replaced by pulse stretcher modulators.

Such a pulse stretcher modulator is shown in FIG. 4. When the inputterminal 52a has applied to it the potential of the negative voltagesupply line 62, the capacitor 535 is extensively discharged, and theinput potential of the inverting input of the operational amplifier isbelow the potential of the noninverting input, so that the output of theoperational amplifier 530 is at positive potential. Thus, the output ofthe operational amplifier provides a 1 signal. The potential of thenoninverting input of the operational amplifier 530 is high, and isdetermined through the resistors 532, 533, 534, whereby the resistor 532is in parallel, in this case, with the resistor 533. The resistor 536 issubstantially small in relation to the resistors 532, 533 and 534. Whena predetermined potential prevails at the input terminal 52a, thecapacitor 535 becomes charged to the potential of the positive voltagesupply line, through the resistors 536, 531 and 537. As a result, thepotential of the inverting input of the operational amplifier 530 rises.When this potential exceeds the potential prevailing at thenon-inverting input, the operational amplifier 530 switches statethrough the coupling resistor 532, and a 0 signal prevails at the outputof this amplifier. At the same time, the potential at the noninvertinginput shifts in the direction toward a negative value which is, in turn,determined by the resistors 533, 534 and 532, whereby the resistor 532is, in this case, in parallel with the resistor 534. The capacitor 535discharges from the original input potential of the input terminal 52ain direction to the potential of the negative voltage supply line 62,through the resistors 537 and 531. When the potential at the invertinginput is below the potential of the noninverting input, then theoperational amplifier 530 switches again state, and provides at itsoutput a 1 signal.

This process is repeated periodically, whereby the pulse repetitionfrequency of the output pulses of the operational amplifier 530 isdependent upon the magnitude of the input potential prevailing at theterminal 52a. When this input potential is sufficiently high, then thecapacitor 535 can no longer discharge sufficiently through the resistor531, so that the output of the operational amplifier 530 remainscontinuously at negative potential.

The pulse stretcher modulator in accordance with FIG. 4 operatessimilarly to a threshold switch. Thus, when the input voltage dropsbelow a predetermined threshold level, then the output provides acontinuous 1 signal. When, on the other hand, the output voltage exceedsan upper threshold level, then the output provides a continuous signal.When the input voltage lies between the lower and upper thresholdlevels, the pulse stretcher modulator provides pulses having arepetition frequency dependent upon the magnitude of the input voltage.The potential difference between the lower and upper threshold levels isdetermined through the relationship between the two resistors 53] and537. The absolute magnitude of the two threshold levels is, on the otherhand, determined by the voltage divider 533, 534, 532.

When two pulse stretcher modulators in accordance with FIG. 4, are usedin place of the two threshold switches 53, 54, then the three controlvalves 34, 36 and 38 are controlled in a pulse-wise manner when theoutput value differs by small amounts from the input value. As a result,the displacement velocity of the control slide 23 and thereby theacceleration of the operating piston 12 become essentially smaller. Withthis arrangement, softer transitions in the motion are realized. For asmaller dead zone and corresponding larger positional accuracy, largerfinal velocities of the control slides are possible. The rest of thefunctional operation is precisely the same as when using the thresholdswitches.

The dead zone is to be as small as possible for attaining a largepositional accuracy of the control slide 23. At the same time, thedisplacement velocity of the control slide is to be, on the other hand,as large as possible. In order that a stable operation of thearrangement may be obtained, the dead zone and the dead time of thevalves must be matched. The two requirements of maximum possibledisplacement velocity and smallest possible dead zone are in conflict.

In the first embodiment of FIG. 1, the displacement velocity of thecontrol slide 23 is larger than the velocity when the control slide ismoved from its 0 position in direction of greater deflection, in thereturn process. This results from the condition that upon deflection ormovement from the 0 position, the spring force is opposed against thehydraulic force in the return arrangement 28, whereas the spring forceadds to the hydraulic force during the return process. The displacementvelocity in the return process must, therefore, take into account thedead zone.

In order to make possible a smaller dead zone, other force relationshipsare selected in the circuit embodiment of FIG. 5. Thus, the hydraulicforce acts on the differential piston 26 only upon deflection ormovement from the 0 position,- but not during the return process. Thismay be attained because in the return process the first control valve 34is basically closed.

To determine whether a deflection process or a return process prevails,the components 70 to 75 are used. The third threshold switch 70determines whether the control slide 23 is either to the right or to theleft of the 0 position, whereas the fourth threshold switch 71determines whether the regulating deviation is either positive ornegative, i.e., whether the output value has already attained the inputvalue or not.

In order that the first control valve 34 becomes opened, all four inputsof the first AND-gate 43 must have I signals. The manner in which the Isignals at the first two inputs are derived, is already described above.These first two inputs are connected with the outputs of the dead centercircuit 50 and the third AND-gate 56. Assume, now, as an example, thatthe control slide 23 becomes moved towards the left, and has not as yetattained the input value. Then the third threshold switch provides a 0signal and the fourth threshold switch 71 also provides a 0 signal,since the output voltage of the output transducer 47 as well as from thesumming device, are negative. In this case, both inverters 72 and 74provide 1 signals which are transmitted, through the OR-gates 73 and 75,to the two remaining inputs of the first AND-gate 43. As soon as theinput value is attained, the regulating error or deviation becomes 0 orpositive, and the fourth threshold switch 71 provides a I signal. Atthis point, a 0 signal lies at the third input of the AND-gate 43, whichis connected with the second OR-gate 75, whereas a 1 signal still liesat the fifth input. As a result, the first control valve 34 becomesclosed. This closing of the valve also remains when the remote controllever 55 is again returned to the 0 position. Upon return of the controlslide 23, the control cylinder 27 can thereby have applied fluid fromthe first control valve 34.

In the second embodiment of FIG. 5, it is also possible to use pulsestretcher modulators in accordance with FIG. 4, instead of the first twothreshold switches 53 and 54.

The control arrangement described above, fulfills, consequently, all ofthe imposed requirements. The velocity of the operating piston 12 is setto a constant value through the remote control lever 55 as well asthrough the control lever 30. This constant value depends on thedeflection or displacement of the remote control lever or of the lever30. When using both stretcher modulators, it is possible to avoidfurthermore accelerations or delays which are too large for smallregulating errors or deviations. When the remote control lever 55 is atits normal inoperative position, then the control slide 23 can beactuated with the aid of the control lever 30. An output value-return isthen made possible to maintain precisely the velocity for the operatingpiston 12, which is set by the remote control lever. The controlarrangement is, thereby, particularly adaptable for automotive cranes,although its area of application is not limited to this field.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofelectro-hydraulic control arrangements differing from the typesdescribed above.

While the invention has been illustrated and described as embodied in anelectro-hydraulic control arrangement, it is not intended to be limitedto the details shown, since various modifications and structural changesmay be made without departing in any way from the spirit of the presentinvention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. An electrohydraulic control arrangement for hydraulic operating meansoperative in two directions comprising, in combination, a control valvewith control slides; two hydraulic transmission lines communieating withsaid operating means and closed by said control slide when in neutralposition in said control valve; inlet line means communicating with oneof said hydraulic transmission lines when said control slide is in afirst operative position; return line means communicating with the otherone of said hydraulic transmission lines when said control slide is in asecond operative position; control piston means movable within a controlcylinder and actuating said control slide; electromagnetically actuatedvalves for applying working fluid to said control cylinder; remotecontrol lever means for providing an adjustable input parameter;regulating amplifier means actuating said electromagnetic valves as afunction of said input parameter; two flow lines communicating with saidcontrol cylinder and connected to saidinlet line means and said returnline means by two of said electromagnetically actuated valves; signalamplifying means connected to said electromagnetically actuated valvesfor actuating said electromagnetically actuated valves; and thresholdswitching means connected between said signal amplifying means and saidregulating amplifying means.

2. The arrangement as defined in claim 1 wherein a first one of saidelectromagnetically actuated valves is connected between said inlet linemeans and said two electromagnetically actuated valves, said first oneof said electromagnetically actuated valves being closed when saidremote control lever means is in position.

3. The arrangement as defined in claim 2 including a close control leverfor actuating said control slide when said first one of saidelectromagnetically actuated valves is closed and said twoelectromagnetically actuated valves are open.

4. The arrangement as define in claim 2 including a dead center circuit;an input parameter transducer actuated by said remote control levermeans; and a first amplifier in said signal amplifying means connectedto said first one of said electromagnetically actuated valves, the inputof said first amplifier being connected through said dead center circuitto said input parameter transducer.

5. The arrangement as defined in claim 4 wherein said dead centercircuit comprises two threshold switching circuits having differentthreshold levels, the input of one threshold switching circuit beingconnected with a first input of the other threshold switching circuit,the output of said one threshold switching circuit being connected to asecond input of the other threshold switching circuit.

6. The arrangement as defined in claim 4 including AND-gates connectedto a second amplifier and a third amplifier in said signal amplifyingmeans; a threshold switching circuit connected to a first input of eachAND-gate, the second inputs of said AND-gates being connected to saiddead center circuit.

7. The arrangement as defined in claim 6 including an AND-gate connectedto the input of said first amplifier, a first input of said AND-gateconnected to said first amplifier being connected to said dead centercircuit, said AND-gate connected in front of said first amplifier beinga first AND-gate and said AND-gates connected to said second and thirdamplifiers being respectively second and third AND-gates; a fourthAND-gate connected between the second input of said first AND- gate andthe outputs of said second and third AND- gates.

8. The arrangement as defined in claim 4 including an amplifying stageconnected in series with the input of said dead center circuit.

9. The arrangement as defined in claim 1 including output parametertransducer means actuated by said control slide; input parametertransducer means actuated by said remote control lever means; andsumming means with inputs connected to said input and output parametertransducer means, the output of said summing means being connected tosaid regulating amplifying means.

10. The arrangement as defined in claim 7 wherein said thresholdswitching circuits and said AND-gates are two-stage, positivefeedback-coupled transistor amplifiers with two transistors ofcomplementary conductivity type.

1 l. The arrangement as defined in claim 10 including base voltagedivider means connected to a first one of said two transistors in saidthreshold switching circuits for setting the threshold voltage of saidthreshold switching circuit; and diode means for applying to the emitterof said first transistor the input voltage signal.

12. The arrangement as defined in claim 10 including diode meansconnected to the emitter of a first transistor of said AND-gates forapplying input voltage signals to the emitter of said first transistorof said AND-gates.

13. The arrangement as defined in claim 4 including second and thirdAND-gates connected to second and third amplifiers in said amplifyingmeans; and pulse stretcher modulator means connected to first inputs ofsaid second and third AND-gates, the second inputs of said AND-gatesbeing connected to said dead center circuit, said pulsestretcher'modulator means controlling intermittently saidelectromagnetically actuated valves when the output signals of saidregulating amplifier means are substantially small, saidelectromagnetically actuated valves being continuously unactuated whenthe output signals of said regulating amplifier means are substantiallylarge.

14. The arrangement as defined in claim 13 wherein said pulse stretchermodulator comprises an operational amplifier with a first resistorconnected between the output of said amplifier and one input thereof,and a second resistor connected between the output of said operationalamplifier and a circuit input thereof; an input resistor connected tothe inverting input of said operational amplifier, on terminal of saidinput resistor being the input signal terminal; and a capacitorconnected between said input resistor and ground potential.

15. The arrangement as defined in claim 9 including a third thresholdswitch connected to the output of said output parameter transducermeans; and a forth threshold switching circuit connected to the outputof said summing means.

16. The arrangement as defined in claim 15 including a first OR-gate anda second OR-gate, the output of said third threshold switching circuitbeing connected to said second OR-gate and to said first OR-gate; afirst inverter circuit connected between said output of said thirdthreshold switching circuit and said first OR-gate; a second invertercircuit connected between the output of said fourth threshold switchingcircuit and said second OR-gate, the output of said fourth thresholdswitching circuit being also connected to said first OR- gate, theoutputs of said OR-gates being connected to the inputs of said firstAND-gate.

17. The arrangement as defined in claim 7 wherein said fourth AND-gatecomprises a NAND-gate.

t t l

1. An electrohydraulic control arrangement for hydraulic operating meansoperative in two directions comprising, in combination, a control valvewith control slides; two hydraulic transmission lines communicating withsaid operating means and closed by said control slide when in neutralposition in said control valve; inlet line means communicating with oneof said hydraulic transmission lines when said control slide is in afirst operative position; return line means communicating with the otherone of said hydraulic transmission lines when said control slide is in asecond operative position; control piston means movable within a controlcylinder and actuating said control slide; electromagnetically actuatedvalves for applying working fluid to said control cylinder; remotecontrol lever means for providing an adjustable input parameter;regulating amplifier means actuating said electromagnetic valves as afunction of said input parameter; two flow lines communicating with saidcontrol cylinder and connected to said inlet line means and said returnline means by two of said electromagnetically actuated valves; signalamplifying means connected to said electromagnetically actuated valvesfor actuating said electromagnetically actuated valves; and thresholdswitching means connected between said signal amplifying means and saidregulating amplifying means.
 2. The arrangement as defined in claim 1wherein a first one of said electromagnetically actuated valves isconnected between said inlet line means and said two electromagneticallyactuated valves, said first one of said electromagnetically actuatedvalves being closed when said remote control lever means is in 0position.
 3. The arrangement as defined in claim 2 including a closecontrol lever for actuating said control slide when said first one ofsaid electromagnetically actuated valves is closed and said twoelectromagnetically actuated valves are open.
 4. The arrangement asdefine in claim 2 including a dead center circuit; an input parametertransducer actuated by said remote control lever means; and a firstamplifier in said signal amplifying means connected to said first one ofsaid electromagnetically actuated valves, the input of said firstamplifier being connected through said dead center circuit to said inputparameter transducer.
 5. The arrangement as defined in claim 4 whereinsaid dead center circuit comprises two threshold switching circuitshaving different threshold levels, the input of one threshold switchingcircuit being connected with a first input of the other thresholdswitching circuit, the output of said one threshold switching circuitbeing connected to a second input of the other threshold switchingcircuit.
 6. The arrangement as defined in claim 4 inCluding AND-gatesconnected to a second amplifier and a third amplifier in said signalamplifying means; a threshold switching circuit connected to a firstinput of each AND-gate, the second inputs of said AND-gates beingconnected to said dead center circuit.
 7. The arrangement as defined inclaim 6 including an AND-gate connected to the input of said firstamplifier, a first input of said AND-gate connected to said firstamplifier being connected to said dead center circuit, said AND-gateconnected in front of said first amplifier being a first AND-gate andsaid AND-gates connected to said second and third amplifiers beingrespectively second and third AND-gates; a fourth AND-gate connectedbetween the second input of said first AND-gate and the outputs of saidsecond and third AND-gates.
 8. The arrangement as defined in claim 4including an amplifying stage connected in series with the input of saiddead center circuit.
 9. The arrangement as defined in claim 1 includingoutput parameter transducer means actuated by said control slide; inputparameter transducer means actuated by said remote control lever means;and summing means with inputs connected to said input and outputparameter transducer means, the output of said summing means beingconnected to said regulating amplifying means.
 10. The arrangement asdefined in claim 7 wherein said threshold switching circuits and saidAND-gates are two-stage, positive feedback-coupled transistor amplifierswith two transistors of complementary conductivity type.
 11. Thearrangement as defined in claim 10 including base voltage divider meansconnected to a first one of said two transistors in said thresholdswitching circuits for setting the threshold voltage of said thresholdswitching circuit; and diode means for applying to the emitter of saidfirst transistor the input voltage signal.
 12. The arrangement asdefined in claim 10 including diode means connected to the emitter of afirst transistor of said AND-gates for applying input voltage signals tothe emitter of said first transistor of said AND-gates.
 13. Thearrangement as defined in claim 4 including second and third AND-gatesconnected to second and third amplifiers in said amplifying means; andpulse stretcher modulator means connected to first inputs of said secondand third AND-gates, the second inputs of said AND-gates being connectedto said dead center circuit, said pulse stretcher modulator meanscontrolling intermittently said electromagnetically actuated valves whenthe output signals of said regulating amplifier means are substantiallysmall, said electromagnetically actuated valves being continuouslyunactuated when the output signals of said regulating amplifier meansare substantially large.
 14. The arrangement as defined in claim 13wherein said pulse stretcher modulator comprises an operationalamplifier with a first resistor connected between the output of saidamplifier and one input thereof, and a second resistor connected betweenthe output of said operational amplifier and a circuit input thereof; aninput resistor connected to the inverting input of said operationalamplifier, on terminal of said input resistor being the input signalterminal; and a capacitor connected between said input resistor andground potential.
 15. The arrangement as defined in claim 9 including athird threshold switch connected to the output of said output parametertransducer means; and a forth threshold switching circuit connected tothe output of said summing means.
 16. The arrangement as defined inclaim 15 including a first OR-gate and a second OR-gate, the output ofsaid third threshold switching circuit being connected to said secondOR-gate and to said first OR-gate; a first inverter circuit connectedbetween said output of said third threshold switching circuit and saidfirst OR-gate; a second inverter circuit connected between the output ofsaid fourth threshold switching cirCuit and said second OR-gate, theoutput of said fourth threshold switching circuit being also connectedto said first OR-gate, the outputs of said OR-gates being connected tothe inputs of said first AND-gate.
 17. The arrangement as defined inclaim 7 wherein said fourth AND-gate comprises a NAND-gate.